sysctls

sysctls

[Andrew Morton]

I note that the networking tree is adding new sysctls:

<<<<<<< HEAD/include/linux/sysctl.h
        NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
=======
        NET_IPV6_OPTIMISTIC_DAD=24,
        NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
>>>>>>> /include/linux/sysctl.h

(Well, it's trying to - there are some git rejects in net-2.6.22)

But we kind-of decided a while back to stop doing that and to
use CTL_UNNUMBERED.

Frankly, I don't 100% remember the thinking - Eric, can you please remind
us?

Re: sysctls

[Eric W. Biederman]

Andrew Morton <akpm@linux-foundation.org> writes:

> I note that the networking tree is adding new sysctls:
>
> <<<<<<< HEAD/include/linux/sysctl.h
>         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
> =======
>         NET_IPV6_OPTIMISTIC_DAD=24,
>         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
>>>>>>>> /include/linux/sysctl.h
>
> (Well, it's trying to - there are some git rejects in net-2.6.22)
>
> But we kind-of decided a while back to stop doing that and to
> use CTL_UNNUMBERED.
>
> Frankly, I don't 100% remember the thinking - Eric, can you please remind
> us?

The thinking is this:

  Binary sysctl numbers are a problem because of patch conflicts like
  the above, and the related user space breakage they cause.

  In practice no one uses binary sysctl numbers.

So the policy should be to add new sysctl's using CTL_UNNUMBERED
(to prevent patch conflicts and user space breakage).

There may be cases where someone actually needs the binary sysctl
interface.  Once there is a demonstrated need we can go back
and very carefully add numbers for these very few cases, with
a strong review process.

Adding binary sysctl numbers should be done as carefully as and with
as much review as adding syscall numbers, and distro kernels and other
stable kernels should never get a sysctl number backport until the
number first reaches Linus's tree.  To avoid difference in meaning
between different kernels.

Given that no one except on BSD uses the binary sysctl interface
anyway my personal preference is to just freeze it and to reduce the
number of binary sysctls we support if possible.

Eric

Re: sysctls

[Neil Horman]

On Wed, Apr 25, 2007 at 01:45:19PM -0600, Eric W. Biederman wrote:
> Andrew Morton <akpm@linux-foundation.org> writes:
> 
> > I note that the networking tree is adding new sysctls:
> >
> > <<<<<<< HEAD/include/linux/sysctl.h
> >         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
> > =======
> >         NET_IPV6_OPTIMISTIC_DAD=24,
> >         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
> >>>>>>>> /include/linux/sysctl.h
> >
> > (Well, it's trying to - there are some git rejects in net-2.6.22)
> >
> > But we kind-of decided a while back to stop doing that and to
> > use CTL_UNNUMBERED.
> >
> > Frankly, I don't 100% remember the thinking - Eric, can you please remind
> > us?
> 
> The thinking is this:
> 
>   Binary sysctl numbers are a problem because of patch conflicts like
>   the above, and the related user space breakage they cause.
> 
>   In practice no one uses binary sysctl numbers.
> 
> So the policy should be to add new sysctl's using CTL_UNNUMBERED
> (to prevent patch conflicts and user space breakage).
> 
> There may be cases where someone actually needs the binary sysctl
> interface.  Once there is a demonstrated need we can go back
> and very carefully add numbers for these very few cases, with
> a strong review process.
> 
> Adding binary sysctl numbers should be done as carefully as and with
> as much review as adding syscall numbers, and distro kernels and other
> stable kernels should never get a sysctl number backport until the
> number first reaches Linus's tree.  To avoid difference in meaning
> between different kernels.
> 
> Given that no one except on BSD uses the binary sysctl interface
> anyway my personal preference is to just freeze it and to reduce the
> number of binary sysctls we support if possible.
> 
> Eric
> -
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I did the optimistic dad sysctl, and have no strict use for numbered sysctls (I
was just unaware of the policy).  I'll work up a patch to use
register_sysclt_table with CTL_UNNUMBERED in the next few days.

Regards
Neil

Re: sysctls

[Andrew Morton]

On Wed, 25 Apr 2007 15:53:19 -0400
Neil Horman <nhorman@tuxdriver.com> wrote:

> I did the optimistic dad sysctl, and have no strict use for numbered sysctls (I
> was just unaware of the policy).  I'll work up a patch to use
> register_sysclt_table with CTL_UNNUMBERED in the next few days.

I don't think you need to add a call to register_sysctl_table(), if that's
what you're proposing.  Just drop the changes to sysctl.h and use CTL_UNNUMBERED
in sysctl.c.

Re: sysctls

[David Miller]

From: Andrew Morton <akpm@linux-foundation.org>
Date: Wed, 25 Apr 2007 14:50:18 -0700

> On Wed, 25 Apr 2007 15:53:19 -0400
> Neil Horman <nhorman@tuxdriver.com> wrote:
> 
> > I did the optimistic dad sysctl, and have no strict use for numbered sysctls (I
> > was just unaware of the policy).  I'll work up a patch to use
> > register_sysclt_table with CTL_UNNUMBERED in the next few days.
> 
> I don't think you need to add a call to register_sysctl_table(), if that's
> what you're proposing.  Just drop the changes to sysctl.h and use CTL_UNNUMBERED
> in sysctl.c.

Ok, I'll take care of this.

Re: sysctls

[Neil Horman]

On Wed, Apr 25, 2007 at 04:47:34PM -0700, David Miller wrote:
> From: Andrew Morton <akpm@linux-foundation.org>
> Date: Wed, 25 Apr 2007 14:50:18 -0700
> 
> > On Wed, 25 Apr 2007 15:53:19 -0400
> > Neil Horman <nhorman@tuxdriver.com> wrote:
> > 
> > > I did the optimistic dad sysctl, and have no strict use for numbered sysctls (I
> > > was just unaware of the policy).  I'll work up a patch to use
> > > register_sysclt_table with CTL_UNNUMBERED in the next few days.
> > 
> > I don't think you need to add a call to register_sysctl_table(), if that's
> > what you're proposing.  Just drop the changes to sysctl.h and use CTL_UNNUMBERED
> > in sysctl.c.
> 
> Ok, I'll take care of this.
Thank you dave.
Neil

Re: sysctls

[David Miller]

From: Andrew Morton <akpm@linux-foundation.org>
Date: Wed, 25 Apr 2007 12:29:24 -0700

> 
> I note that the networking tree is adding new sysctls:
> 
> <<<<<<< HEAD/include/linux/sysctl.h
>         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
> =======
>         NET_IPV6_OPTIMISTIC_DAD=24,
>         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
> >>>>>>> /include/linux/sysctl.h
> 
> (Well, it's trying to - there are some git rejects in net-2.6.22)

I knew this was going to happen because of Yoshifuji's
security fix, the conflict is trivial to resolve.

I'll rebase the net-2.6.22 tree later today since all
we should have before 2.6.21-final is the netlink
OOPS'er fix Alexey just posted.

Re: sysctls

[Eric W. Biederman]

David Miller <davem@davemloft.net> writes:

> From: Andrew Morton <akpm@linux-foundation.org>
> Date: Wed, 25 Apr 2007 12:29:24 -0700
>
>> 
>> I note that the networking tree is adding new sysctls:
>> 
>> <<<<<<< HEAD/include/linux/sysctl.h
>>         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
>> =======
>>         NET_IPV6_OPTIMISTIC_DAD=24,
>>         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
>> >>>>>>> /include/linux/sysctl.h
>> 
>> (Well, it's trying to - there are some git rejects in net-2.6.22)
>
> I knew this was going to happen because of Yoshifuji's
> security fix, the conflict is trivial to resolve.
>
> I'll rebase the net-2.6.22 tree later today since all
> we should have before 2.6.21-final is the netlink
> OOPS'er fix Alexey just posted.

David for clarity do you happen to know of anyone using binary
sysctl values?

In particular is there any reason not to use CTL_UNNUMBERED
for new networking sysctls?

Eric

Re: sysctls

[David Miller]

From: ebiederm@xmission.com (Eric W. Biederman)
Date: Wed, 25 Apr 2007 14:06:34 -0600

> David for clarity do you happen to know of anyone using binary
> sysctl values?

None at all.

> In particular is there any reason not to use CTL_UNNUMBERED
> for new networking sysctls?

Neil said he would send me a patch to do that.

Thanks.

Re: sysctls

[Eric W. Biederman]

David Miller <davem@davemloft.net> writes:

> From: ebiederm@xmission.com (Eric W. Biederman)
> Date: Wed, 25 Apr 2007 14:06:34 -0600
>
>> David for clarity do you happen to know of anyone using binary
>> sysctl values?
>
> None at all.
>
>> In particular is there any reason not to use CTL_UNNUMBERED
>> for new networking sysctls?
>
> Neil said he would send me a patch to do that.

Thanks. I just wanted to be certain I wasn't missing something,
when asking people not to use binary sysctl values.

Eric